Examples of workpieces conveyed in manufacturing factories and the like include metal molds for manufacturing metal parts, materials before molding of the metal parts, and the metal parts. Some of these workpieces have weights of several hundred kilograms to several tons. Such a heavy workpiece is conveyed to a predetermined position in such a manner that the heavy workpiece is suspended by, for example, a crane installed in a factory and is then moved by a worker in a horizontal direction. In a case where the worker performs operations of moving and stopping such a heavy load, the heavy workpiece may hit an inner wall, a device, and the like in the factory, and this may damage the heavy workpiece, the inner wall, the device, and the like.
To solve this problem, the heavy workpiece may be conveyed by using a large robot. In the conveyance operation, the heavy workpiece needs to be conveyed to the predetermined position with a high degree of accuracy. To satisfy this need, it is necessary to use a large robot including a highly stiff arm. However, if the highly-stiff arm is adopted, the manufacturing cost of the large robot becomes extremely high. The operation of lifting up the heavy load is hardly performed in the factory. Therefore, installing the large robot including the highly-stiff arm is difficult in terms of cost. Known as a conveyance system that solves such a cost problem is a conveyance system described in PTL 1.
The conveyance system of PTL 1 includes a balancer and a robot. A holding portion that holds the heavy workpiece is provided at a tip end portion of the balancer. A seat is formed at the tip end portion of the balancer, and the robot holds the seat to move the holding portion of the balancer to the predetermined position. A balance weight is attached to the balancer, and the load on the robot is reduced by the balance between the weight of the heavy workpiece and the balance weight.